The corneal endothelium is engaged in continuously pumping towards the anterior chamber the fluid which leaks into the corneal stroma, thereby keeping the cornea relatively dehydrated and transparent. We propose to continue our long range research on the basic mechanism of fluid and electrolyte transport by the endothelium. A better understanding of this process may help in the prevention and treatment of blindness of corneal origin. As in other epithelia, the transport of fluid appears to be secondary to the transport of ions. We theorize that ionic transport occurs as a result of the function of a hydrogen for sodium exchanger, the sodium pump, and perhaps chloride permeation sites at the lateral membranes, and a coupled sodium-bicarbonate symport and perhaps potassium sites and a chloride for bicarbonate antiport at the apical membrane. In addition, cells would have permeation sites for divalent cations. We will investigate the location and properties of such postulated permeation sites with novel techniques. Specifically, we propose to: 1) investigate location and characteristics of ionic permeation sites with patch and whole cell clamp techniques; 2): investigate the osmotic permeability of the endothelium with a computer-linked automatic specular microscope, and study cell volume regulatory processes; 3) refine and update existing theoretical models for fluid and ion transport across the endothelium; 4) refine measurements of transendothelial fluid flow and extend our studies on the rate and time-course of fluid pumping, and study time-transient changes in the transendothelial potential and other endothelial electrical parameters. In most of the above, typical studies will include effects of ambient factors such as solution composition and temperature, concentrations changes, transport inhibitors or ionic cell membrane permeability modifiers.